Electronic devices formed on flexible substrates are used in applications that require non-planar forms or that require mechanical manipulation in different configurations. For example, some devices are designed to be folded or unfolded. Other devices are located on curved surfaces. A variety of technologies are under development for such applications, including organic electronics, inkjet deposition, polymer layers, and flexible substrate materials such as polymers and paper. Such technologies enable applications such as flexible or curved displays, antennas, solar cells, batteries, sensors, and biomedical devices.
Flexible substrates or printed circuit boards are an important component of flexible electronic devices. Currently, silk-screened metal wire conductors formed on a polymer substrate are used as flexible connectors in many electronic systems. Such methods typically have limited resolution. Other patterned conductors are formed using photolithographic processes on flexible materials, but such methods are typically difficult because of material and process compatibility issues and the expense of such processes. Such prior-art methods can also produce devices with a relatively limited radius of curvature, thereby limiting the applications and configurations to which the technology is applied.
There is also a need for high-density electronic devices that incorporate three-dimensional circuit structures. Such structures increase the number of computing elements per volume but are typically expensive to construct. Other applications integrate optical devices such as lenses or reflectors into optoelectronic devices. Such devices typically include multiple, separate elements that are separately manufactured and then carefully aligned and integrated at a relatively high resolution and cost.
Very fine patterns of conductive elements, such as metal wires or conductive traces are known. For example, U.S. Patent Application Publication No. 2011/0007011 teaches a capacitive touch screen with a mesh electrode, as do U.S. Patent Application Publication No. 2010/0026664, U.S. Patent Application Publication No. 2010/0328248, and U.S. Pat. No. 8,179,381, which are hereby incorporated in their entirety by reference. As disclosed in U.S. Pat. No. 8,179,381, fine conductor patterns are made by one of several processes, including laser-cured masking, inkjet printing, gravure printing, micro-replication, and micro-contact printing. In particular, micro-replication is used to form micro-conductors formed in micro-replicated channels. The transparent micro-wire electrodes include micro-wires between 0.5μ and 4μ wide and a transparency of between approximately 86% and 96%.
Conductive micro-wires can be formed in micro-channels embossed in a substrate, for example as taught in CN102063951, which is hereby incorporated by reference in its entirety. As discussed in CN102063951, a pattern of micro-channels is formed in a substrate using an embossing technique. Embossing methods are generally known in the prior art and typically include coating a curable liquid, such as a polymer, onto a rigid substrate. A pattern of micro-channels is imprinted (impressed or embossed) onto the polymer layer by a master having an inverted pattern of structures formed on its surface. The polymer is then cured. A conductive ink is coated over the substrate and into the micro-channels, the excess conductive ink between micro-channels is removed, for example by mechanical buffing, patterned chemical electrolysis, or patterned chemical corrosion. The conductive ink in the micro-channels is cured, for example by heating or exposure to HCl vapor. In an alternative method described in CN102063951, a photosensitive layer, chemical plating, or sputtering is used to pattern conductors, for example, using patterned radiation exposure or physical masks. Unwanted material (e.g. photosensitive resist) is removed, followed by electro-deposition of metallic ions in a bath.
Multi-level masks are used with photo-lithography to form thin-film devices, for example as disclosed in U.S. Pat. No. 7,202,179. An imprinted 3D template structure is provided over multiple thin films formed on a substrate. The multiple levels of the template structure are used as masks for etching the thin films. This approach requires the use of a mask and multiple photo-lithographic steps.
The use of integrated circuits with electrical circuitry is well known. Various methods for providing integrated circuits on a substrate and electrically connecting them are also known. Integrated circuits can have a variety of sizes and packages. In one technique, Matsumura et al., in U.S. Patent Application Publication No. 2006/0055864, describes crystalline silicon substrates used for driving LCD displays. The application describes a method for selectively transferring and affixing pixel-control devices made from first semiconductor substrates onto a second planar display substrate. Wiring interconnections within the pixel-control device and connections from buses and control electrodes to the pixel-control device are shown.
Printed circuit boards are well known for electrically interconnecting integrated circuits and often include multiple layers of conductors with vias for electrically connecting conductors in different layers. Circuit boards are often made by etching conductive layers deposited on laminated fiberglass substrates. However, such etching processes are expensive and the substrates are not transparent and therefore of limited use in applications for which transparency is important, for example display and touch-screen applications.
Flexible substrates are also known in the art and are used with other devices, such as displays. U.S. Pat. No. 6,501,528 discloses a stacked display device with a folded substrate. U.S. Pat. No. 7,792,558 describes a mobile communication device with bent connector wires and U.S. Pat. No. 8,017,884 illustrates an integrated touch panel and electronic device. U.S. Pat. No. 5,520,112 describes a folded substrate and a dual-sided printing process. Such substrates, structures, and methods demonstrate an on-going need in the industry for manufacturing methods incorporating devices and flexible substrates.